NWP in the Met Office

transcript

Topics to be covered...

1. Describing the atmosphere2. Using observations 3. Model mathematics4. Operational models purposes5. Model outputs

OBSERVATIONS

HUMAN FORECASTER

CUSTOMERS

NUMERICAL FORECASTS

The Weather Prediction Process

ARCHIVES

Unified Model

• Met. Office has several requirements:

• local forecasting

• global forecasting

• climate modelling

• ocean and wave modelling

• a common model:

• shares code and operating structure

• is modular where differences are necessary

• gives considerable savings in maintenance cost

Unified Model configurations

Met Office models

Based on Unified Model

• Global

• North Atlantic and European model

• 4km and 12km Mesoscales

• Crisis Area Mesoscale Models

• Stratospheric

• FOAM ocean forecasting models

Met Office models

Other models including

• Wave (Global, European, UK Waters)

• Surge

• NAME

• SSFM

Fundamentals of NWP

1. Specify atmospheric initial conditions in a numerical form

2. Use equations describing atmospheric physical processes to predict how the initial state will evolve

3. Output the forecast in a useful form for the user

1. Describing the atmosphere

Specify the properties in the grid box

from observational data (temp, pressurehumidity, wind etc.)

Grid length

Grid point

Unified Model is a gridpoint model

GM Vertical resolution – 50 levels

In boundary layer levels are terrain-following

In free atmosphere levels are height coordinates

In between levels are a combination of the 2

Lowest model levels present/new 70Lat 10m/2.5m for windat 20m/5m for temp

17.5 km

Global, North Atlantic & European, mesoscale models

Global Model (GM)

Horizontal Resolution: Mid-latitude 40km

Timestep: 20mins

Vertical levels: 50, then 70

Grid:Standard lat/long type, with filtering near the poles

Global Model (GM)

Horizontal Resolution: Mid-latitude 40km

Timestep: 20mins

Vertical levels: 50, then 70

Grid:Standard lat/long type, with filtering near the poles

Mesoscale Model (MES)

Horizontal Resolution: 12km/4km Timestep: 5/ 1.7 mins

Vertical levels: 38, eventually 70

Grid:Rotated lat/long (‘Equatorial Lat-long Fine-mesh’ - ELF)

Mesoscale Model (MES)

Horizontal Resolution: 12km/4km Timestep: 5/ 1.7 mins

North Atlantic & European Model (NAE)

Horizontal Resolution: 12km Timestep: ~5 mins

North Atlantic & European Model (NAE)

Horizontal Resolution: 12km Timestep: ~5 mins

2. Using observations

Data assimilation

• GM uses 4-D VAR; 12km MES and NAE 3-D VAR

• 4km MES has no data assimilation yet• Model is run for an assimilation period

prior to the forecast

• 6 hrs for GM model

• 3 hrs for the MES and NAE

Data assimilation

• Observations firstly quality controlled against

• climate data

• model background field

• nearby obs.

• Then inserted into the run at or near their validity time to nudge the model towards reality

Using observations

Models try to make the best possible use of observations

synopsynop

sonde sonde

Observations arechecked for qualityand interpolated ontothe model grid points

Different types of datahave different areas ofinfluence

Moisture Observation Pre-processing System (MOPS)

Used only in 12km MES/NAE

Latent heating and cooling important in driving mesoscale systems

MOPS is an analysis of humidity, cloud and precipitation for 12km MES and NAE

Soil moisture in the GM

No longer reset weekly to climatology New soil moisture nudging scheme Not as complex as MOPS Produced verifiable improvement, especially surface

temperatures

3. Model Mathematics

Model variables

• PRIMARY PROGNOSTIC variables are explicitly calculated using the primitive equations

• ANCILLARY FIELDS are fixed lower boundary conditions

• SECONDARY PROGNOSTIC variables are calculated at each timestep from the prognostic variables.

Primary prognostic variables

• Horizontal and vertical wind components• potential temperature• specific humidity• cloud water and ice• surface pressure• surface temperature• soil temperature• canopy water content• snow depth

Ancillary fields

• land/sea mask• soil type• vegetation type• grid-box mean and variance of

orography• sea surface temperature• proportion of sea-ice cover• sea-ice thickness• sea surface currents

Prognostic Prognostic variables in variables in coupled coupled atmosphere/atmosphere/ocean ocean modelsmodels

Global model orography

NAE Model orography

12km / 4km MES Model orography

Model variables

• PRIMARY PROGNOSTIC variables are explicitly calculated using the primitive equations

• SECONDARY PROGNOSTIC variables are calculated by the parameterisation schemes

Model variables

• primary prognostic variables

•horizontal and vertical wind components

•potential temperature

•specific humidity

•cloud water and ice

•surface pressure

•surface temperature

•soil temperature

•canopy water content

•snow depth

• secondary prognostic variables

•boundary layer depth

•sea surface roughness

•convective cloud amount

•convective cloud base

•convective cloud top

•layer cloud amount

•ozone mixing ratio

Parametrised processes

1. Layer cloud and precipitation2. Convective cloud and precipitation3. Radiative processes4. Surface and sub-surface processes5. Gravity wave drag

1. Layer cloud and precipitation

Convective cloud model

Terminal outflow of mass, heat,water vapour and cloud water/ice

Mixing at cloudedge

Subsidence outside cloudsto compensate for upward

motion within clouds 0 C°

2. Convective cloud and precipitation

3. Radiative processes

LongwaveradiationShortwave

radiation

Diffuseshortwave

Layer cloud

Cumulus.cloud

4. Surface and sub-surface processes

Heat, moistureand momentum

transport byturbulent eddies

SeaLand

Sublimation

Heat fluxthrough soil

Netradiation

Evaporationfrom

vegetation

Heat fluxfrom sea

Heat fluxfrom ice

Sublimationfrom ice

Evaporationfrom soil

Evaporationfrom sea

Drainageinto soil

Interception ofppn by canopy

Sea ice

5. Gravity wave drag

= Const

Tropopause

Wavebreaking

Boundary conditions

• Lower and upper boundaries

• Lateral boundaries

• Land & sea: ancillary fields

• Stratosphere: ‘lid’ to model

• required in MES and NAE models

• primary prognostic variables required at each grid point

• NAE and 12km MES supplied from global model

• 4km MES supplied from NAE

• possible source of error

4. Purposes of Operational Models

Global model

• 4 times daily• Run times … 00Z, 06Z,12Z, 18Z • Data accepted up to T+1 hour 45 min• Out to T+144 (6 days) at 00Z and 12Z, T+48

at 06Z and 18Z• Takes 2hr 15 mins to run out to T+144, 1hr

15min for T+48

Global model

• Used for:-

• regional synoptic guidance

• medium range guidance

• civil aviation products

• mesoscale model boundary conditions

North Atlantic & European model

• Run times … 00, 06, 12 and 18Z • Takes boundary conditions from Global Model (previous GM run)

• Run partly overlaps with the GM• Out to T+48

North Atlantic & European model

• Used for:-

• wider range of products to international customers

• Improved Synoptic development guidance

• Better for rapid developments and extremes

• Boundary conditions for 4km MES

Advantages of NAE Model

• Large domain

• Captures developing systems over North Atlantic

• Covers all of Europe and European Nimrod area

• includes some other model areas

• Higher resolution than GM (12km-v-40km)

• Better for rapid developments and extremes

12km Mesoscale model

• Run times … 00Z, 06Z, 12Z and 18Z • Takes boundary conditions from Global Model

• Runs in parallel with the GM (starts 10 mins later)

• Out to T+48 (2 days)

12km Mesoscale model

• Used for:-

• UK local detail (ppn, cloud,temp,wind)

• Input to other systems (SSFM, and Nowcasting systems etc.)

4km MES model

• Run times … 03Z, 09Z, 15Z, 21Z• Takes boundary conditions from NAE Model • Out to T+36• No data assimilation

Model Dependencies (simplified!)

GLOBALGLOBAL

12KM MES12KM MES

GLOBAL WAVEGLOBAL WAVE

FOAMFOAM

UK WATERS WAVEUK WATERS WAVE

EUROPEAN WAVEEUROPEAN WAVE

SURGESURGE

SHELF SEASSHELF SEAS

NAMENAME

Scheduling must account for all dependencies and timeliness requirements of each model run

SSFMSSFM

NAE MODELNAE MODEL

4KM MES4KM MES

Any questions?GM, NAE and MES output.http://www-nwp/~meso/current_mesglob_charts.html

NWP Gazettehttp://www.metoffice.gov.uk/research/nwp/publications/nwp_gazette/index.html

NWP technical reportshttp://www.metoffice.gov.uk/research/nwp/publications/papers/technical_reports/index.html4km mesoscale runs:http://www-nwp/~meso/current_uk4mesglob_charts.html

NWP in the Met Office

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